Alberto Treviño <alberto <at> byu.edu> writes: > The problem I've seen with this feature is that Windows guests end up taking > all of their available memory once they are up and running. For example, > booting Windows XP in KVM 82 show a steady increase in memory. Then about > the time the login box is about to appear, memory usage jumps to the maximum > allowed to the VM (512 MB in this case). I remember reading somewhere > Windows would try to initialize all memory during boot, causing KVM to > allocate all memory. VMware, however (and I don't know about VirtualBox) > knows about this and works around it, making sure memory isn't all allocated > during the Windows boot process. Windows does zero all memory at boot, and also runs a idle-priority thread in the background to zero memory as it is freed. This way it is far less likely to need to zero a page to satisfy a memory allocation request. Whether or not this is still a win now that people care about power consumption is an open question. I suspect the difference of behavior between KVM and VMware is related to VMware's page sharing. All those zeroed pages can be collapsed into one COW zero page. I wouldn't be surprised to learn that VMware has heuristics in the page sharing code specifically for windows guests. Perhaps KSM would help you? Alternately, a heuristic that scanned for (and collapsed) fully zeroed pages when a page is faulted in for the first time could catch these. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
